In a cutting machine, which is known under its trade name Partner K650 Super, the filter system comprises a pre-filter, a main filter, and a spill filter. The pre-filter includes a ring shaped piece of felt positioned around a perforated, oval filter housing. The main filter is an oiled foam filter and has also the shape of a ring and is arranged close to the inner side of the perforated oval filter housing. Inside the main filter is the spill filter which comprises a strainer which prevents objects falling into the motor during service. In order that the machine will operate without problems, the pre-filter can be pulled off and shaken clean with every tanking operation and be replaced or thoroughly washed after a certain period of operation. The main filter is removed by unscrewing the filter housing. Each time the main filter is taken out of the filter housing, the housing has to be cleaned. Moreover, cleaning of the pre-filter and of the filter housing is troublesome and dirty, which does not promote correct handling. There exists therefore a great risk that the engine is damaged because the filter system is not handled strictly in accordance with the instruction book. By experience it is also known that the service intervals of this type of machine are short. Another disadvantage is that the filter system gives very poor silencing of noise from the intake air, which can be very severe as far as two-stroke engines are concerned.
In another cutting machine, which is known under the trade name Husqvarna 272K, the pre-filter is an oiled foam filter provided in the upper front part of the power unit, while the main filter is a paper filter, which is also located in the upper part of the power unit, at the rear of the pre-filter. From the pre-filter chamber air is led rearwardly to the main filter chamber through a substantially horizontal conduit, which takes up a substantial part of the available space in the top part of the unit with the result that the space is not used efficiently. Moreover, the requirement for easy access to the spark plug has been solved in a manner which neither promotes an effective use of spaces which could be available for air cleaning and noise silencing, nor provides optimal silencing of the intake air noise. In spite of the fact that it is a purpose of the design to make the system easy to handle, the cleaning of the pre-filter chamber is still a problem.